package com.oig.common.util;
/**
 * 描述: Twitter的分布式自增ID雪花算法snowflake (Java版)
 *
 * snowflake的结构如下(每部分用-分开):
 *
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000
 * 第一位为未使用，接下来的41位为毫秒级时间(41位的长度可以使用69年)，
 * 然后是5位datacenterId和5位workerId(10位的长度最多支持部署1024个节点） ，
 * 最后12位是毫秒内的计数（12位的计数顺序号支持每个节点每毫秒产生4096个ID序号）
 *
 * 一共加起来刚好64位，为一个Long型。(转换成字符串长度为18)
 *
 * snowflake生成的ID整体上按照时间自增排序，
 * 并且整个分布式系统内不会产生ID碰撞（由datacenter和workerId作区分），并且效率较高。
 * 据说：snowflake每秒能够产生26万个ID。
 **/
public class SnowFlakeUtil {
    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1620809640000L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 2;   //机器标识占用的位数2^2=4个机器
    private final static long DATACENTER_BIT = 1;//数据中心占用的位数2^1=2个数据中心

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~ (-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long dataCenterId;  //数据中心
    private long machineId;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳

    public SnowFlakeUtil(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.dataCenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getNewMill();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | dataCenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }

    private long getNextMill() {
        long mill = getNewMill();
        while (mill <= lastStmp) {
            mill = getNewMill();
        }
        return mill;
    }

    private long getNewMill() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        SnowFlakeUtil snowFlake = new SnowFlakeUtil(1, 3);

        for (int i = 0; i < (1 << 12); i++) {
            System.out.println(snowFlake.nextId());
            System.out.println(Long.toBinaryString(snowFlake.nextId()));
        }

    }
}
